Benzaldehyde carbonyl group

LADH the ratio is 2. This is interpreted as ziuc(n) polarization of the benzaldehyde carbonyl group resulting in Lewis acid catalysis. 

The aldol condensation is versatile in that the enolate anion of one carbonyl compound can be made to add to the carbonyl carbon of another, provided that the reaction partners are carefully selected. Consider, for example, the reaction between acetaldehyde and benzaldehyde, when treated with base. Only acetaldehyde can form an enolate anion (benzaldehyde has no a-hydrogen). If the enolate ion of acetaldehyde adds to the benzaldehyde carbonyl group, a mixed aldol condensation occurs. 

To understand the effect of a carbonyl group attached directly to the ring consider Its polarization The electrons m the carbon-oxygen double bond are drawn toward oxy gen and away from carbon leaving the carbon attached to the nng with a partial posi tive charge Using benzaldehyde as an example... 

Because the carbon atom attached to the ring is positively polarized a carbonyl group behaves m much the same way as a trifluoromethyl group and destabilizes all the cyclo hexadienyl cation intermediates m electrophilic aromatic substitution reactions Attack at any nng position m benzaldehyde is slower than attack m benzene The intermediates for ortho and para substitution are particularly unstable because each has a resonance structure m which there is a positive charge on the carbon that bears the electron withdrawing substituent The intermediate for meta substitution avoids this unfavorable juxtaposition of positive charges is not as unstable and gives rise to most of the product... 

The mechanism for formation of benzaldehyde diethyl acetal which proceeds m two stages is presented m Figure 17 9 The first stage (steps 1-3) involves formation of a hemiacetal m the second stage (steps 4-7) the hemiacetal is converted to the acetal Nucleophilic addition to the carbonyl group characterizes the first stage carbocation chemistry the second The key carbocation intermediate is stabilized by electron release from oxygen... 

Increased single bond character in a carbonyl group is associated with a decreased carbon—oxygen stretching frequency Among the three compounds benzaldehyde 2 4 6 trimethoxybenzaldehyde and 2 4 6 trinitrobenzaldehyde which one will have the lowest frequency carbonyl absorption" Which one will have the highest" ... 

Benzaldehyde is a versatile iatermediate because of its reactive aldehyde hydrogen, its carbonyl group, and the benzene ring. 

To identify the carbonyl compound and the ylide required to produce a given alkene, mentally disconnect the double bond so that one of its carbons is derived from a carbonyl group and the other is derived from an ylide. Taking styrene as a representative example, we see that two such disconnections are possible either benzaldehyde or formaldehyde is an appropriate precursor. 

The carbonyl group reactivities in thiophenes and benzenes are very similar, as shown by the similar rates of alkaline hydrolysis of esters and by the great similarity of the thiophenealdehydes to benzaldehyde in numerous carbonyl group reactions. This has been ascribed to the counteracting —I- -M effects of the thienyl group in this kind of reactions. ... 

One further comparison aromatic aldehydes, such as benzaldehyde, are less reactive in nucleophilic addition reactions than aliphatic aldehydes because the electron-donating resonance effect of the aromatic ring makes the carbonyl group less electrophilic. Comparing electrostatic potential maps of formaldehyde and benzaldehyde, for example, shows that the carbonyl carbon atom is less positive (less blue) in the aromatic aldehyde. 

Neither benzaldehyde nor formaldehyde can form an enolate ion to add to another partner, yet both compounds have an unhindered carbonyl group. 

More recently the stereoselectivity of the addition of sulfinyl anions to carbonyl groups was improved by introducing a sulfide group in the a-position30,31. The sulfoxide ( + )-(S)-(4-methylphcnylsulfinyl)(4-methylphenylthio)metliane was added to benzaldehyde to give the adduct 1 as a mixture of three diastereomers [(S5,15,27 )/(SS,17 ,2/J)/(S5,15,25) 55 30 15] which could be transformed into the corresponding a-methoxyaldehydc 4 in 67% yield with 70 % ee. The same reaction, when applied to phenylacetaldehyde, led to a product in 43 % yield with lower ee (46%). 

An example of this effect, called conformational transmission, is found in ergost-7-en-3-one (5) and cholest-6-en-3-one (6), where 6 condenses with benzaldehyde 15 times faster than 5. The reaction site in both cases is the earbonyl group, and the rate increases because moving the double bond from the 7 to the 6 position causes a change in conformation at the carbonyl group (the difference in the side chain at C-17 does not affect the rate). 

The formation of ethers such as 1806 by EtsSiH 84b can also be catalyzed by trityl perchlorate to convert, e.g., benzaldehyde in 84% yield into dibenzyl ether 1817 [48]. The combination of methyl phenethyl ketone 1813 with O-silylated 3-phenyl-n-pro-panol 1818, in the presence of trityl perchlorate, leads to the mixed ether 1819 in 68% yield [48] (Scheme 12.15). Instead of trityl perchlorate, the combination of trityl chloride with MesSiH 84a or EtsSiH 84b and sodium tetrakis[3,5-bis-(trifluoro-methyl)phenyl]borane as catalyst reduces carbonyl groups to ethers or olefins [49]. Employing TMSOTf 20 as catalyst gives very high yields of ethers. Thus benzaldehyde reacts with O-silylated allyl alcohol or O-silylated cyclohexanol to give the... 

Reduction of carbonyl groups Terpene and aromatic aldehydes (lOOppm) were reduced by microalgae. In a series of chlorinated benzaldehyde, m - or p-chlorobenzaldehyde reacted faster than the o-derivative. Due to toxicity, the substrate concentrations are difficult to increase. Asymmetric reductions of ketones by microalgae were reported. Thus, aliphatic " and aromatic " ketones were reduced. 

Figure 8.33 Strong, sharp band at 1700 cnY1 indicating a carbonyl group. Absorption bands on the high side of 3000 cnY1 and a series of weak bands between 1700 and 2000 cnY1 indicating a benzene ring. Possibly benzaldehyde, or a similar compound.

When the reaction with substituted benzaldehydes is conducted in the presence of ammonia, the a-amino carboxylic acids are formed [11], The corresponding reaction involving bromoform is less effective and, for optimum yields, the addition of lithium chloride, which enhances the activity of the carbonyl group, is required. In its absence, the overall yields are halved. The reaction of dichlorocarbene with ketones or aryl aldehydes in the presence of secondary amines produces a-aminoacetamides [12, 13] (see Section 7.6). 

Amide group reduction probably occurs by the mechanism shown in Scheme 3. Two-electron transfer without protonation would give dianion 3. Elimination of LiNMe2 from 3 would give 4 (an acyl anion equivalent) and protonation of 4 at the carbonyl group would give benzaldehyde. 

The carbon atom of the carbonyl group of benzaldehyde is less electrophilic than carbon atom of the carbonyl group present in... 

Upon formation of the trans adduct of benzaldehyde with TADDOL, the mframolecular hydrogen bond is shortened by 0.128 A, and the acidity of the substrate binding hydroxy function is increased. The length of the intermolccular hydrogen bond to the carbonyl group is 1.825 A. 

---